You will have to check the syntax of this because I'm not installing VB6 just for this (or much else to be honest).
Dim along As Variant
along = 123549512
Dim longAsString As String
longAsString = CStr$(long)
Dim res as String
res = Left$(longAsString, 5)
[Edited to change
Str$
to
CStr$
.. the former includes a space for the sign of the number, the latter does not. Alternatively could have taken the string from the 2nd character, but that is not as clear)
[Edited to fix the syntax error with Left$ spotted and corrected by @RichardDeeming - thank you]